1. Field of the Invention
This invention relates to the connectorization of flat cable and, in particular, to the strain-relief anchoring thereof, as secured to an associated connector.
2. Background of the Invention
In connectorizing flat cable of the type having a plurality of laterally disposed conductors arranged in either a single array, or in multiple overlying/underlying arrays, it is imperative that the connectorized ends of the cable conductors be isolated from any possible detrimental tensile or shear forces. Such forces, without reliable strain relief being provided, can often lead to seriously impaired cable conductor-connector contact connections, if not actual open-circuits, regardless whether such connections are of the soldered, or solderless type. Appreciable stress can often be imparted on a connectorized length of cable during not only the subsequent reeling and de-reeling thereof, but also during its installation in electrical equipment or in buildings.
Thus, regardless of the manner in which a given flat cable is connectorized, some form of strain relief must be employed in order to insure the integrity of the established interconnections. One of the most simple techniques employed heretofore to effect cable strain relief is to thread an end portion of a terminated cable through two or more openings or slots formed in either a rearward integral portion of a connector housing, or in an auxiliary member secured to a rearward portion of the latter.
Such a slotted member forces that portion of the cable threaded therethrough into a tortuous or serpentine path, with the resulting sharp bends imparted to the cable effectively anchoring it from longitudinal movement relative to the associated connector. Concomitantly, this form of strain relief also isolates the electrical connections from otherwise possible detrimental shear forces during normal handling of the connectorized cable. One form of this type of cable strain relief is disclosed in J. N. Worman U.S. Pat. No. 3,997,234, wherein the strain relief openings are actually formed in a so-called plug package handle (often referred to as a paddle board) secured to, rather than formed as an integral part of, a connector housing per se.
A disadvantage of a tortuous path-defined type of strain relief is that it is often quite difficult, depending primarily on the degree of stiffness, and thickness, of the cable, to thread an end portion of the latter through the necessary strain relief-forming slots or openings. In addition, it is likewise difficult to determine initially how much of a terminated end portion of the cable should be threaded through the strain relief-defining slots so that the normally stripped ends of the conductors may be consistently brought into not only aligned, but co-extensive, relationship with the respective connector receptacles or contacts, as required to effect either solder or solderless type connections therebetween.
Another form of cable strain relief is provided by utilizing an independent multi-sectioned clamping device, typically formed of two complementary, interlockable molded plastic sections, dimensioned so as to provide a frictional-engaging passageway therebetween for an end region of a terminated cable. In one prior strain relief device of this type, each complementary plastic section thereof is formed with a laterally disposed, centrally positioned rib that normally supports a U-shaped resilient insert, such as of rubber. These inserts are employed to frictionally engage and clamp opposite sides of a terminating section of cable interposed therebetween. The molded sections of the strain relief device are also constructed such that when assembled and interlocked, a laterally disposed forward boss thereof is adapted to be received within an accommodating recess formed in a rearward housing portion of an associated connector.
Each strain relief section of the prior type in question is also formed at one end with an outwardly extending U-shaped locking detail, and at the other end with a protruding locking shoulder. The shoulder in each strain relief section is adapted to engage a mating surface of the U-shaped detail in the complementary section, when the two sections are assembled with a terminating section of a cable interposed therebetween. One form of such a multi-sectioned strain relief device is sold by the AMP Corporation, with one particular version thereof, without a pair of resilient inserts being employed therewith, being disclosed in W. B. Fritz et al. U.S. Pat. No. 4,149,026.
Disadvantageously, it has been found that such unadjustable two-piece strain relief devices, even when resilient inserts are employed therewith, do not always reliably and consistently effect the clamping of an end portion of a terminated flat cable therebetween. This results, in part, from the fact that the resilient inserts tend to lose their resiliency and, hence, their initial clamping force capability, with time.
This has been found to present a particular problem when connectorized flat cable is employed in telephone undercarpet wiring installations, where continuous running lengths of such cable may often be on the order of 15 to 35 ft., as distinguished from lengths of from less than one foot to no more than several feet in many telephone switching and computer equipment wiring applications. It thus becomes readily apparent that when relatively long lengths of connectorized flat cable are either drawn off a supply reel, or otherwise uncoiled, and then laid out along a floor in accordance with a prescribed path, the electrically connected conductor ends of such cables necessarily are subjected to appreciable tensile, as well as shear, forces in the absence of some type of effective strain relief being provided.
Another disadvantage in having to utilize resilient inserts is that they double the number of parts required to assemble a complimentary multi-sectioned strain relief device. This not only increases manufacturing costs, but increases the possibility of the inserts becoming separated from the main molded sections of the device before their interlocked assembly.